Compounds of antimony and germanium as catalysts for melt polycarbonate

ABSTRACT

The present invention relates to a synthetic method in which one or more diaryl carbonates is reacted with one or more dihydroxy aromatic compounds in the presence of a transesterification catalyst under melt polymerization conditions to afford a product polycarbonate. The transesterifcation catalysts used according to the method of the present invention are alkali metal salts and alkaline earth metal salts of antimony oxides or germanium oxides in combination with tetraalkyl ammonium or tetraalkyl phosphonium compounds which serve as co-catalysts. The antimony oxide derivative “tartar emetic”, structure IV, was shown to possess excellent activity as a transesterifcation catalyst for the preparation of polycarbonate under melt polymerization conditions. The catalysts employed according to the method of the present invention provide polycarbonates having substantial molecular weight (M n ˜7000-10000 daltons) and reduced levels of Fries rearrangement product relative to conventionally prepared melt polycarbonate having a similar molecular weight.

BACKGROUND OF THE INVENTION

This invention relates to salts of antimony and germanium oxides usefulas transesterification catalysts in melt polymerization reactions ofdihydroxy aromatic compounds with diaryl carbonates. The inventionfurther relates to a method for the preparation of polycarbonates usingalkali and alkaline earth metal salts of antimony oxides and germaniumoxides. The method may be used to provide a product polycarbonatecomprising a lower level of Fries product than is provided by otherknown methods employing conventional melt transesterification catalysts.

Increasingly, polycarbonate is being prepared by the melt reaction of adiaryl carbonate with a dihydroxy aromatic compound in the presence of atransesterification catalyst, such as sodium hydroxide. In this “melt”process, reactants are introduced into a reactor capable of stirring aviscous polycarbonate melt at temperatures in excess of 300° C.Typically, the reaction is run at reduced pressure to facilitate theremoval of by-product hydroxy aromatic compound formed as the diarylcarbonate reacts with the dihydroxy aromatic compound and growingpolymer chains.

The Fries rearrangement is a ubiquitous side reaction taking placeduring the preparation of polycarbonate using the melt process. Theresultant “Fries product” serves as a site for branching of thepolycarbonate chains thereby affecting flow and other properties of thepolycarbonate. Although, a low level of Fries product may be toleratedin the product polycarbonate produced by the melt process, the presenceof higher levels of Fries product may negatively impact performancecharacteristics of the polycarbonate, such as moldability and toughness.Currently, alkali metal hydroxides, such as sodium hydroxide, areemployed as catalysts in the preparation of polycarbonate using the meltprocess. Alkali metal hydroxides, although effective catalysts in termsof rates of conversion of starting materials to product polycarbonate,tend to produce relatively high levels of Fries rearrangement product.Thus, melt polymerization methodology useful for the preparation ofpolycarbonate in which the formation of Fries product has been minimizedrepresents a long sought goal among those wishing to practice suchmethodology.

It would be a significant advantage to prepare polycarbonate by a meltpolymerization method which provides high rates of polymerization whileminimizing the amount of Fries product formation.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method for the preparation ofpolycarbonate, said method comprising contacting at least one diarylcarbonate with at least one dihydroxy aromatic compound in the presenceof a transesterification catalyst comprising at least one alkali metalor alkaline earth metal salt of an antimony or germanium oxide andoptionally a co-catalyst, under melt polymerization conditions to afforda product polycarbonate.

In one aspect the method of the present invention affords a productpolycarbonate having a lower level of Fries rearrangement product thanpolycarbonate of similar molecular weight prepared using a conventionalmelt transesterification catalyst.

The present invention further relates to a method of preparingpolycarbonate under melt polymerization conditions by reacting at leastone dihydroxy aromatic compound with at least one diaryl carbonate inthe presence of at least one salt of antimony oxide or germanium oxide,said salt having structure I

(MO_(n))_(m)(A)_(p)(R¹)_(q)  I

wherein M is antimony or germanium, n is an integer in a range from 0 to4, m is an integer in a range from 1 to 2, A is independently at eachoccurrence an alkali metal ion or an alkaline earth metal ion, p is aninteger in a range from 1 to 4, R¹ is an organic ligand, and q is aninteger in a range from 0 to 2.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of preferred embodiments of the inventionand the examples included therein. In the following specification andthe claims which follow, reference will be made to a number of termswhich shall be defined to have the following meanings:

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

As used herein the term “polycarbonate” refers to polycarbonatesincorporating structural units derived from at least one dihydroxyaromatic compounds and includes copolycarbonates and polyestercarbonates.

As used herein, the term “melt polycarbonate” refers to a polycarbonatemade by a process comprising the transesterification of a diarylcarbonate with a dihydroxy aromatic compound in the presence of atransesterification catalyst.

“BPA” is herein defined as bisphenol A or2,2-bis(4-hydroxyphenyl)propane.

“Catalyst system” as used herein refers to the catalyst or catalyststhat catalyze the transesterification of the dihydroxy aromatic compoundwith the diaryl carbonate in the preparation of melt polycarbonate.

“Catalytically effective amount” refers to the amount of the catalyst atwhich catalytic performance is exhibited.

As used herein the term “Fries product” is defined as a structural unitof the product polycarbonate which upon hydrolysis of the productpolycarbonate affords a carboxy-substituted dihydroxy aromatic compoundbearing a carboxy group adjacent to one or both of the hydroxy groups ofsaid carboxy-substituted dihydroxy aromatic compound. For example, inbisphenol A polycarbonate prepared by a melt reaction method in whichFries reaction occurs, the Fries product affords carboxy bisphenol A,II, upon complete hydrolysis of the product polycarbonate.

The terms “Fries product” and “Fries group” are used interchangeablyherein.

The terms “Fries reaction” and “Fries rearrangement” are usedinterchangeably herein.

As used herein the term “hydroxy aromatic compound” means a phenol, suchas phenol, p-cresol or methyl salicylate, comprising a single reactivehydroxy group and is used interchangeably with the term “phenolicby-product”.

As used herein the term “aliphatic radical” refers to a radical having avalence of at least two comprising a linear or branched array of carbonatoms which is not cyclic. Examples of aliphatic radicals includemethylene; ethylene; 1,2-dimethylethylene; hexamethylene; and the like.

As used herein the term “aromatic radical” refers to a radical having avalence of at least two, said radical comprising at least one aromaticgroup. The aromatic radical may be composed entirely of carbon andhydrogen atoms, or may comprise heteroatoms such as nitrogen, oxygen andsulfur.

As used herein the term “cycloaliphatic radical” refers to a radicalhaving a valance of at least two comprising an array of atoms which iscyclic but which is not aromatic. The array may include heteroatoms suchas nitrogen, sulfur and oxygen or may be composed exclusively of carbonand hydrogen.

It should be understood that as used herein, the terms “aliphaticradical”, “aromatic radical” and “cycloaliphatic radical” include bothsubstituted and unsubstituted embodiments of said radicals. Typicalsubstituents according to the present invention for the substitutedforms of aliphatic, aromatic and cycloaliphatic radicals include C₁-C₂₀alkyl, C₃-C₂₀ cycloalkyl, C₄-C₂₀ aryl, halogen, hydroxy, carbonyl,nitro, cyano, C₁-C₂₀ alkoxy, C₁-C₂₀ alkoxycarbonyl, and the like.

It should be understood that the terms “mmHg” and “torr” are usedinterchangeably herein as units of pressure.

It has been discovered that the use of salts of antimony oxides orgermanium oxides as polymerization catalysts in the melttransesterification reaction of a dihydroxy aromatic compound such asbisphenol A with a diaryl carbonate such as diphenyl carbonate, providesa product polycarbonate comprising a reduced level of Friesrearrangement product. This reduction in the amount of Friesrearrangement is highly desirable in that it results in increasedductility of the product polycarbonate and avoids uncontrolled branchingwhich may occur at sites of Fries rearrangement. Uncontrolled branchingmay limit the utility of the product polycarbonate by reducing theductility of the product polycarbonate. Salts of antimony oxides orgermanium oxides employed as transesterification catalysts according tothe method of the present invention produced less Fries rearrangementproduct than did alkali metal hydroxide transesterification catalysts,such as sodium hydroxide.

In one embodiment, the present invention provides a catalyst system forthe production of polycarbonate under melt polymerization conditions,wherein the polycarbonate has a number average molecular weight, M_(n)of at least about 8000 daltons and a reduced content of Fries productsrelative to a polycarbonate of comparable molecular weight preparedusing an alkali metal hydroxide transesterification catalyst. Inparticular, it is desirable to have Fries product of less than 3000 ppm,preferably less than 2000 ppm, more preferably less than 1000 ppm, evenmore preferably less than 500 ppm.

The transesterification catalyst according to the present inventioncomprises at least one alkali metal or alkaline earth salt of antimonyoxide or germanium oxide, having structure I

(MO_(n))_(m)(A)_(p)(R¹)_(q)  I

wherein M is antimony or germanium, n is an integer in a range from 0 to4, m is an integer in a range from 1 to 2, A is independently at eachoccurrence an alkali metal ion or an alkaline earth metal ion, p is aninteger in a range from 1 to 4, R¹ is an organic ligand, and q is aninteger in a range from 0 to 2.

In one embodiment of the present invention structure I represents aseries of antimony oxide derivatives wherein M is an antimony atom (Sb),n is an integer having a value of 3, m is an integer having a value of 1or 2, A is an alkali metal cation or an alkaline earth metal cation, andq is an integer having a value of 0, there being no organic ligand R¹.Suitable examples of such antimony oxide derivatives include NaSbO₃,LiSbO₃, KSbO₃, and Mg(SbO₃)₂. In one embodiment of the present inventionthe transesterification catalyst comprises sodium antimonate, NaSbO₃.

In an alternate embodiment of the present invention structure I is analkali metal or alkaline earth salt derivative of antimony oxide whereinM is Sb, n is 0, m is 2, A is an alkali metal ion or an alkaline earthmetal ion, p is 1 or 2, q is 2, and R¹ is an organic ligand havingstructure III.

Thus, in one embodiment of the present invention the transesterificationcatalyst is the tartarate derivative IV, sometimes referred to as“tartar emetic”, a compound with a rich history as a medicinal agent.

As has been noted, the transesterification catalyst according to thepresent invention is in some embodiments an alkali metal or alkalineearth salt of or germanium oxide, having structure I. In theseembodiments, with respect to structure I, M is a germanium atom (Ge), nis an integer having a value of 3 or 4, m is an integer having a valueof 1, A is an alkali metal ion or an alkaline earth metal ion, p is aninteger having a value of 1 or 2, and q is zero, there being no organicligand. Suitable examples of such germanium oxide derivatives, the metagermanate and ortho germanate derivatives of Na₂GeO₃, K₂GeO₃, Li₂GeO₃,MgGeO₃, and Mg₂GeO₄. In one embodiment of the present invention thetransesterification catalyst comprises sodium meta germanate, Na₂GeO₃.

The present invention relates to salts of antimony oxides or germaniumoxides useful as catalysts under melt polymerization conditionscomprising contacting at least one dihydroxy aromatic compound and atleast one diaryl carbonate. Dihydroxy aromatic compounds which areuseful in preparing polycarbonates according to the method of thepresent invention may be represented by the general formula V

wherein R² is independently at each occurrence a halogen atom, nitrogroup, cyano group, C₁-C₂₀ alkyl group, C₄-C₂₀ cycloalkyl group, orC₆-C₂₀ aryl group; r and 5 are independently integers 0-3; and W is abond, an oxygen atom, a sulfur atom, a SO₂ group, a C₁-C₂₀ aliphaticradical, a C₆-C₂₀ aromatic radical, a C₆-C₂₀ cycloaliphatic radical orthe group

wherein R³ and R⁴ are independently a hydrogen atom, C₁-C₂₀ alkyl group,C₄-C₂₀ cycloalkyl group, or C₄-C₂₀ aryl group; or R³ and R⁴ togetherform a C₄-C₂₀ cycloaliphatic ring which is optionally substituted by oneor more C₁-C₂₀ alkyl, C₆-C₂₀ aryl, C₅-C₂₁ aralkyl, C₅-C₂₀ cycloalkylgroups or a combination thereof.

Suitable bisphenols V according to the method of the present inventioninclude bisphenol A; 2,2-bis(4-hydroxy-3-methylphenyl)propane;2,2-bis(3-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-3-isopropylphenyl)propane;1,1-bis(4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane; and1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

In one aspect of the present invention, the diaryl carbonate usedaccording to the method of the present invention has structure VI

wherein R⁵ is independently at each occurrence a halogen atom, nitrogroup, cyano group, C₁-C₂₀ alkyl group, C₁-C₂₀ alkoxy carbonyl group,C₄-C₂₀ cycloalkyl group, or C₆-C₂₀ aryl group; and t and v areindependently integers 0-5.

Diaryl carbonates VI suitable for use according to the method of thepresent invention are illustrated by diphenyl carbonate,bis(4-methylphenyl)carbonate, bis(4-chlorophenyl)carbonate,bis(4-fluorophenyl)carbonate, bis(2-chlorophenyl)carbonate,bis(2,4-difluorophenyl)carbonate, bis(4-nitrophenyl)carbonate,bis(2-nitrophenyl)carbonate, and bis(methyl salicyl)carbonate (CAS No.82091-12-1).

In one embodiment, structural units of the product polycarbonate derivedfrom the dihydroxy aromatic compound are comprised entirely ofstructural units derived from bisphenol A, and structural units derivedfrom the diaryl carbonate are derived entirely from diphenyl carbonate.

Optionally, one or more branching agents may be included during the meltpolymerization reaction according to the method of the present inventionas a means of effecting the controlled branching of the productpolycarbonate as is sometimes desirable in applications, such as in blowmolding of beverage bottles, requiring a high degree level of meltstrength. Suitable branching agents include1,1,1-tris(4-hydroxyphenyl)ethane (THPE) and 1,3,5-trihydroxybenzene.

In the process of the present invention, an endcapping agent mayoptionally be used. Suitable endcapping agents include hydroxy aromaticcompounds such as phenol, p-tert-butylphenol, p-cumylphenol, cardanoland the like.

When an endcapping agent is employed said endcapping agent is preferablyused in an amount corresponding to between about 0.001 and about 0.10moles, preferably about 0.01 to about 0.08 moles per mole of thedihydroxy aromatic compound employed.

The catalyst having structure I is employed in an amount correspondingto between about 1×10⁻⁸ and 2.5×10⁻⁴, preferably between about 1×10⁻⁷and 2.5×10⁻⁵ moles of catalyst per mole of dihydroxy aromatic compoundemployed. When the amount of catalyst employed is less than 1×10⁻⁸ moleof catalyst per mole of dihydroxy aromatic compound employed, reactionrates may be reduced to such an extent that no appreciable molecularweight gain is observed. Generally, it is preferred that the numberaverage molecular weight (M_(n)) of the product polycarbonate be atleast about 8000 daltons. When the amount of catalyst is in excess ofabout 2.5×10⁻⁴ moles per mole of dihydroxy aromatic compound employed,rates of Fries rearrangement may be excessive and high levels ofuncontrolled branching may occur.

The transesterification catalyst may be added in a variety of formsaccording to the method of the present invention. The catalyst may beadded as a solid, for example a powder, or it may be dissolved in asolvent, for example water or alcohol. In one embodiment, the catalystis added to the reaction system in the form of an aqueous solution. ThepH of the aqueous solution is preferably at or near the pH of a freshlyprepared solution, which varies depending on the identity of thecatalyst used.

If the catalyst is not soluble in water or only sparingly soluble inwater, the catalyst may be dissolved in a solution comprising aquaternary ammonium compound, a quaternary phosphonium compound, or amixture thereof, and the solution comprising the catalyst and said oniumcompound may be used.

The use of a quaternary ammonium compound, a quaternary phosphoniumcompound, or a mixture thereof, as a co-catalyst is not limited toinstances in which the catalyst has low solubility and is introducedinto the reaction mixture as an aqueous solution. Quaternary ammoniumcompounds, quaternary phosphonium compounds, and mixtures thereof, maybe employed as co-catalysts and may be introduced into the reactionmixture in a variety of forms; as solids, in solution, or as a melt.Examples of suitable quaternary ammonium compounds include, but are notlimited to ammonium hydroxides having alkyl groups, aryl groups andalkaryl groups, such as tetraamethylammonium hydroxide (TMAH) andtetrabutylammonium hydroxide (TBAH). Suitable phosphonium compoundsinclude, but are not limited to tetraethylphosphonium hydroxide,tetrabutylphosphonium hydroxide, and tetrabutylphosphonium acetate.

If present, the quaternary ammonium compound, the quaternary phosphoniumcompound, or a mixture thereof, is preferably used in amounts of fromabout 1×10⁻² to about 1×10⁻⁶, preferably about 1×10⁻² to about 1×10⁻⁵moles per mole of dihydroxy aromatic compound. The quaternary oniumcompounds may be used to enhance or modify the activity of the antimonyor germanium oxide derivative employed as the primary catalyst.

In some instances the reaction mixture may further comprise a metalhydroxide, for example, an alkali metal hydroxide such as sodiumhydroxide. The free metal hydroxide may be added to enhance the activityof the alkali metal or alkaline earth metal salt of an antimony orgermanium oxide employed as the primary catalyst, or may be present as acontaminant in the primary catalyst itself. If present, the free metalhydroxide is preferably present in an amount in an amount correspondingto between about 1×10⁻⁸ and 2.5×10⁻⁴ moles of catalyst per mole ofdihydroxy aromatic compound employed.

The reaction conditions of the melt polymerization are not particularlylimited and may be conducted in a wide range of operating conditions.Hence, the term “melt polymerization conditions” will be understood tomean those conditions necessary to effect reaction between the diarylcarbonate and the dihydroxy aromatic compound of the present invention.The reaction temperature is typically in the range of about 100 to about350° C., more preferably about 180 to about 310° C. The pressure may beat atmospheric pressure, supraatmospheric pressure, or a range ofpressures from atmospheric pressure to about 15 torr in the initialstages of the reaction, and at a reduced pressure at later stages, forexample in the range of about 0.2 to about 15 torr. The reaction time isgenerally about 0.1 hours to about 10 hours.

The melt polymerization may be accomplished in one or more stages, as isknown in the art with other catalysts. The catalyst and co-catalysts ofthe present invention may be added in the same stage or differentstages, if the melt polymerization is conducted in more than one stage.The optional co-catalyst may be added at any stage, although it ispreferred that it be added early in the process. When utilized, theco-catalyst is preferably utilized in an amount corresponding to betweenabout 1 and about 500 molar equivalents, based on the moles of catalystI utilized.

In a further preferred embodiment, the process is conducted as a twostage process. In the first stage of this embodiment, the optionalco-catalyst of the present invention is introduced into the reactionsystem comprising the dihydroxy aromatic compound and the diarylcarbonate. The first stage is conducted at a temperature of 270° C. orlower, preferably 80 to 250° C., more preferably 100 to 230° C. Theduration of the first stage is preferably 0 to 5 hours, even morepreferably 0 to 3 hours at a pressure from about atmospheric pressure toabout 100 torr, with a nitrogen atmosphere preferred.

In a second stage, the catalyst having structure I is introduced intothe product from the first stage and further polycondensation isconducted. The catalyst may be added in its entire amount in the secondstage, or it may be added in batches in the second and subsequent stagesso that the total amount is within the aforementioned ranges.

It is preferable in the second and subsequent stages of thepolycondensation step for the reaction temperature to be raised whilethe reaction system is reduced in pressure compared to the first stage,thus bringing about a reaction between the dihydroxy aromatic compoundand the diaryl carbonate. Thus there is formed initially a polycarbonateoligomer which upon further polycondensation reaction at 240 to 320° C.under reduced pressure of 5 mm Hg or less, and preferably 1 mm Hg orless, affords polycarbonate having a number average molecular weight ofabout 8000 daltons or greater.

If the melt polymerization is conducted in more than one stage, as notedabove, it is preferable to add a co-catalyst, such astetramethylammonium hydroxide, tetrabutylammonium hydroxide,tetrabutylphosphonium hydroxide, or tetrabutylphosphonium acetate, in anearlier stage than the catalyst of the present invention. In particular,it is preferable to add the co-catalyst to the reactor before thetemperature reaches 220° C., preferably before it reaches 200° C.

The reaction can be conducted as a batch or a continuous process. Anydesired apparatus can be used for the reaction. The material and thestructure of the reactor used in the present invention is notparticularly limited as long as the reactor has an ordinary capabilityof stirring and is equipped for the removal of by-product hydroxyaromatic compound formed during the course of the polymerization. It ispreferable that the reactor is capable of stirring in high viscosityconditions as the viscosity of the reaction system is increased in laterstages of the reaction.

Thus, in a further embodiment, the present invention provides a methodfor preparing polycarbonates, which comprises the steps of

(a) heating a dihydroxy aromatic compound and a diaryl carbonate for atime period sufficient to form a melt, and thereafter introducing acatalyst composition comprising a catalytically effective amount of acompound having structure I and optionally a co-catalyst selected fromtetraalkylammonium and tetraalkylphosphonium compounds;

(b) oligomerizing the melt mixture formed in step (a) in a reactionsystem comprising at least one continuous reactor in series, whereinsaid reactor is operated at a temperature of about 210° C. to about 290°C., and wherein the product from the reactor has a number averagemolecular weight of about 1000 to about 5500 daltons; and

(c) polymerizing the product from step (b) in a reaction systemcomprising at least one continuous polymerization reactor in series,wherein said reactor is operated at a temperature of about 280° C. to315° C., wherein the product from step (c) has a number averagemolecular weight of at least about 8000 daltons.

Additives may also be added to the polycarbonate product as long as theydo not adversely affect the properties of the product. These additivesinclude a wide range of substances that are conventionally added to thepolycarbonates for a variety of purposes. Specific examples include heatstabilizers, epoxy compounds, ultraviolet absorbers, mold releaseagents, colorants, antistatic agents, slipping agents, anti-blockingagents, lubricants, antifogging agents, natural oils, synthetic oils,waxes, organic fillers, flame retardants, inorganic fillers and anyother commonly known class of additives.

The polycarbonate obtained in accordance with the present invention maybe used after being mixed with conventional additives, such asplasticizers, pigments, lubricants, mold release agents, stabilizers andorganic fillers. It is also possible to blend the polycarbonate withother polymers, including but not limited to, olefins polymers such asABS and polystyrenes, polyesters, polyacrylates, polyethersulfones,polyamides, and polyphenylene ethers.

EXAMPLES

The following examples are set forth to provide those of ordinary skillin the art with a detailed description of how the methods claimed hereinare evaluated, and are not intended to limit the scope of what theinventors regard as their invention. Unless indicated otherwise, partsare by weight, temperature is in ° C.

To facilitate observations and for purity, melt transesterificationreactions were carried out in a 1 Liter glass batch reactor equippedwith a solid nickel helical agitator. The reactor bottom had a breakawayglass nipple for removal of the final melt. To remove any sodium fromthe glass the reactor was soaked in 3N HCl for at least 12 hours,followed by a soak in 18 Mohm water for at least 12 hours. The reactorwas then dried in an oven overnight and stored covered until use. Thetemperature of the reactor was maintained using a fluidised sand bathwith a PID controller. The temperature was measured near the reactor andsand bath interface. The pressure over the reactor was controlled by anitrogen bleed into the vacuum pump downstream of the distillatecollection flasks and measured at higher pressures (760 mmHg-40 mmHg)with a mercury barometer and at lower pressures (40 mmHg-1 mmHg) with anEdwards pirani gauge.

The reactor was charged with solid Bisphenol-A (General ElectricPlastics Japan Ltd., 0.6570 mol) and solid diphenyl carbonate (GeneralElectric Plastics Japan Ltd., 0.7096 mol) prior to assembly. The reactorwas then assembled, sealed, and the atmosphere was exchanged withnitrogen three times. With the final nitrogen exchange, the reactor wasbrought to near atmospheric pressure and submerged into the fluidisedbath which was at 180° C. After five minutes agitation was begun at 250rpm. After an additional ten minutes the reactants were fully melted andthe mixture was assumed to be homogeneous. Tetramethyl ammoniumhydroxide (TMAH) (Sachem, 1.64×10⁻⁴ mole in 740 microliters of water)was added and the catalyst of the invention (0.5×10⁻⁶ to 5×10⁻⁶ molescatalyst per mole bisphenol A) was added to the mixture as a solution indeionized (18 Mohm) water (660 microliters). After the catalyst wasadded, timing began and the temperature was ramped to 210° C. in fiveminutes. Once at temperature, the pressure was reduced to 180 mmHg andphenol distillate was immediately observed. After 25 minutes thepressure was again reduced to 100 mmHg and maintained for 45 minutes.The temperature was then ramped to 240° C. in five minutes and thepressure was lowered to 15 mmHg. These conditions were maintained for 45minutes. The temperature was then ramped to 270° C. in five minutes andthe pressure was lowered to 2 mmHg. These conditions were maintained for10 minutes. The temperature was then ramped to the final finishingtemperature in five minutes and the pressure was reduced to 1.1 mmHg.The finishing temperature was 310° C. After 30 minutes the reactor wasremoved from the sand bath and the product polymer melt was poured intoliquid nitrogen to quench the reaction.

Number average molecular weight (M_(m)) was obtained by gel permeationchromatography (GPC) analysis of the product polycarbonate. Standards ofpolystyrene were used to construct a universal calibration against whichpolycarbonate could be measured using the Mark-Houwink equation. Thetemperature of the columns was 25° C. and the mobile phase waschloroform.

Fries content (ppm) was determined by KOH mediated hydrolysis of theproduct polycarbonate. The amount of Fries product for each of the meltpolycarbonates listed in Table 1 was determined as follows. First, 0.50grams of polycarbonate was dissolved in 4.0 ml of THF (containingp-terphenyl as internal standard). Next, 3.0 ml of 18% KOH in methanolwas added to this solution. The resulting mixture was stirred for twohours at this temperature. Next, 1.0 ml of acetic acid was added, andthe mixture was stirred for 5 minutes. Potassium acetate was allowed tocrystallize over 1 hour. The solid was filtered off and the resultingfiltrate was analyzed by liquid chromoatograph using p-terphenyl as theinternal standard.

Data are gathered in Table 1 which demonstrate the superiority of thecatalysts used according to the method of the present invention relativeto conventional catalysts. Conventional catalyst performance wasillustrated using sodium hydroxide in Comparative Examples 1 and 2(CE-1, CE-2). In Comparative Examples 1 and 2 and in Examples 1-7 thecatalyst was used in an amount corresponding to from about 5×10⁻⁶ toabout 0.5×10⁻⁶ moles of primary catalyst per mole bisphenol A. In allcases a co-catalyst, TMAH, was also present in an amount correspondingto about 2.5×10⁻⁴ mole TMAH per mole bisphenol A. The productpolycarbonate was in all instances bisphenol A polycarbonate. In Table 1the column heading “Primary Catalyst” indicates the specifictransesterification catalyst of the invention employed, or, in the caseof Comparative Examples 1 and 2, the known transesterification catalystsodium hydroxide, NaOH. “M_(n)” denotes number average molecular weightin daltons. The column heading “Fries” indicates the amount of Friesrearrangement product present in the product polycarbonate. “Fries”values are given in parts per million (ppm).

TABLE 1 Example Primary Catalyst Formula M_(n) Fries Primary CatalystConcentration was 5 × 10⁻⁶ moles per mole BPA CE-1 Sodium Hydroxide NaOH8800 3200 Example 1 Sodium Antimonate NaSbO₃ 7427 252 Example 2 Sodiummeta germanate Na₂GeO₃ 8880 779 Example 3 “Tartar emetic” IV 9530 1201Primary Catalyst Concentration was 1 × 10⁻⁶ moles per mole BPA CE-2Sodium Hydroxide NaOH 8200 415 Example 4 Sodium meta germanate Na₂GeO₃9136 404 Example 5 “Tartar emetic” IV 9800 650 Primary CatalystConcentration was 0.5 × 10⁻⁶ moles per mole BPA Example 6 Sodium metagermanate Na₂GeO₃ 7524 136 Example 7 “Tartar emetic” IV 8812 440

The results in Table 1 clearly illustrate the effectiveness of thecatalysts of the present invention as melt polymerization catalysts ascompared to sodium hydroxide (CE-1, CE-2). At a catalyst loading of5×10-6 moles primary catalyst per mole BPA employed, the achievement ofrelatively high molecular weight (M_(n) at least about 8800 daltons)results in the generation of a substantial amount (about 3200 ppm) ofundesired Fries rearrangement product when sodium hydroxide is employed.In contrast, catalysts of the present invention (Examples 2 and 3)provide product polycarbonate having M_(n) greater than 8800 daltonswith substantially reduced levels of Fries rearrangement product. Sodiumantimonate (Example 1) appears to be somewhat less effective than theother catalysts of the present invention. Notwithstanding its somewhatlower catalytic activity of sodium antimonate, a significant molecularweight build was observed in Example 1 and the level of Fries productwas low.

A second series of melt polymerizations was run employing 1×10⁻⁶ molesprimary catalyst per mole of BPA, (See Comparative Example 2 andExamples 4 and 5). The catalysts of the present invention provided muchhigher molecular weight materials than did sodium hydroxide (CE-2).Levels of Fries rearrangement product were slightly higher in Examples 4and 5 than in Comparative Example 2. Because Fries content is frequentlya function of molecular weight, the Fries levels observed in Examples 4and 5 are considered low relative to those observed in ComparativeExample 2.

Example 7 illustrates the effectiveness of “tartar emetic”, structureIV, as a transesterification catalyst according to the method of thepresent invention at a concentration of 0.5×10⁻⁶ moles per mole BPA.

This invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What is claimed is:
 1. A method for the preparation of polycarbonatesaid method comprising contacting at least one diaryl carbonate with atleast one dihydroxy aromatic compound in the presence of atransesterification catalyst and optionally a co-catalyst, under meltpolymerization conditions to afford a polycarbonate, saidtransesterification catalyst comprising at least one alkali metal oralkaline earth metal salt of antimony or germanium said salt havingstructure I (MO_(n))_(m)(A)_(p)(R¹)_(q)  I wherein M is antimony orgermanium, n is an integer in a range from 0 to 4, m is an integer in arange from 1 to 2, A is independently at each occurrence an alkali metalion or an alkaline earth metal ion, p is an integer in a range from 1 to4, R¹ is an organic ligand having structure III

and q is an integer in range from 1 to
 2. 2. A method according to claim1, wherein M is Sb, n is 0, m is 2, A is an alkali metal ion or analkaline earth metal ion, p is 1 or 2, and q is
 2. 3. A method accordingto claim 2 wherein said alkali metal ion or an alkaline earth metal ionis selected from the group consisting of Na, Li, K, and Mg ions.
 4. Amethod according to claim 3 wherein said alkali metal ion or an alkalineearth metal ion is selected from the group consisting of sodium ion andpotassium ion.
 5. A method according to claim 4 wherein said catalysthas structure IV


6. A method according to claim 1, wherein M is Ge and Sb, n is 0, m is2, A is an alkali metal ion or an alkaline earth metal ion, p is ½ or 1,and q is
 2. 7. A method according to claim 6 wherein said alkali metalion or an alkaline earth metal ion is selected from the group consistingof Na, Li, K, and Mg ions.
 8. A method according to claim 7 wherein saidalkali metal ion or an alkaline earth metal ion is selected from thegroup consisting of sodium ion and potassium ion.
 9. A method accordingto claim 1 wherein said dihydroxy aromatic compound is a bisphenolhaving structure V

wherein R² is independently at each occurrence a halogen atom, nitrogroup, cyano group, C₁-C₂₀ alkyl group, C₄-C₂₀ cycloalkyl group, orC₆-C₂₀ aryl group; r and s are independently integers 0-3; and W is abond, an oxygen atom, a sulfur atom, a SO₂ group, a C₁-C₂₀ aliphaticradical, a C₆-C₂₀ aromatic radical, a C₆-C₂₀ cycloaliphatic radical orthe group

wherein R³ and R⁴ are independently a hydrogen atom, C₁-C₂₀ alkyl group,C₄-C₂₀ cycloalkyl group, or C₄-C₂₀ aryl group; or R³ and R⁴ togetherform a C₄-C₂₀ cycloaliphatic ring which is optionally substituted by oneor more C₁-C₂₀ alkyl, C₆-C₂₀ aryl, C₅-C₂₁ aralkyl, C₅-C₂₀ cycloalkylgroups or a combination thereof.
 10. A method according to claim 9wherein said bisphenol is selected from the group consisting ofbisphenol A; 2,2-bis(4-hydroxy-3-methylphenyl)propane;2,2-bis(3-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-3-isopropylphenyl)propane;1,1-bis(4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane; and1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.
 11. A methodaccording to claim 1 wherein said diaryl carbonate has structure VI

wherein R⁵ is independently at each occurrence a halogen atom, nitrogroup, cyano group, C₁-C₂₀ alkyl group, C₁-C₂₀ alkoxy carbonyl group,C₄-C₂₀ cycloalkyl group, or C₆-C₂₀ aryl group; and t and v areindependently integers 0-5.
 12. A method according to claim 11 whereinsaid diaryl carbonate is selected from the group consisting of diphenylcarbonate, bis(4-methylphenyl)carbonate, bis(4-chlorophenyl)carbonate,bis(4-fluorophenyl)carbonate, bis(2-chlorophenyl)carbonate,bis(2,4-difluorophenyl)carbonate, bis(4-nitrophenyl)carbonate,bis(2-nitrophenyl)carbonate, and bis(methyl salicyl)carbonate.
 13. Amethod according to claim 1 wherein said contacting at least one diarylcarbonate with at least one dihydroxy aromatic compound in the presenceof a transesterification catalyst under melt polymerization conditionsis carried out in the presence of one or more branching agents.
 14. Amethod according to claim 13 wherein said branching agent is1,1,1-tris(4-hydroxyphenyl)ethane.
 15. A method according to claim 1wherein said contacting at least one diaryl carbonate with at least onedihydroxy aromatic compound in the presence of a transesterificationcatalyst under melt polymerization conditions is carried out in thepresence of at least one endcapping agent.
 16. A method according toclaim 15 wherein said endcapping agent is a hydroxy aromatic compound.17. A method according to claim 16 wherein said hydroxy aromaticcompound is selected from the group consisting of phenol,p-tert-butylphenol, p-cumylphenol, and cardanol.
 18. A method accordingto claim 1 wherein said transesterification catalyst is employed in anamount corresponding to between 1×10⁻⁸ and 2.5×10⁻⁴ moles catalyst permole dihydroxy aromatic compound.
 19. A method according to claim 1wherein said co-catalyst is selected from the group consisting ofquaternary ammonium compounds, quaternary phosphonium compounds, andmixtures thereof.
 20. A method according to claim 19 wherein saidquaternary ammonium compounds are selected from the group consisting oftetramethyl ammonium hydroxide and tetrabutyl ammonium hydroxide, andsaid quaternary phosphonium compounds are selected from the groupconsisting of tetrabutyl phosphonium acetate and tetrabutylphosphoniumhydroxide.
 21. A method for the preparation of bisphenol A polycarbonatesaid method comprising contacting at least one diaryl carbonate withbisphenol A in the presence of a transesterification catalyst andoptionally a co-catalyst, at a temperature in a range between about 180°C. and about 310° C. and a pressure in a range between about 760 andabout 1 torr to afford a product polycarbonate, said transesterificationcatalyst comprising at least one alkali metal or alkaline earth metalsalt of antimony or germanium, said salt having structure I(MO_(n))_(m)(A)_(p)(R¹)_(q)  I wherein M is antimony or germanium, n isan integer in a range from 0 to 4, m is an integer in a range from 1 to2, A is independently at each occurrence an alkali metal ion or analkaline earth metal ion, p is an integer in a range from 1 to 4, R¹ isan organic ligand having structure III

and q is an integer in a range from 1 to
 2. 22. A method according toclaim 21, wherein M is Sb, n is 0, m is 2, A is an alkali metal ion oran alkaline earth metal ion, p is 1 or 2, and q is
 2. 23. A methodaccording to claim 22, wherein said alkali metal ion or an alkalineearth metal ion is selected from the group consisting of Na, Li, K, andMg ions.
 24. A method according to claim 23 wherein said alkali metalion or an alkaline earth metal ion is selected from the group consistingof sodium ion and potassium ion.
 25. A method according to claim 21wherein said catalyst has structure IV


26. A method according to claim 21 wherein said diaryl carbonate hasstructure VI

wherein R⁵ is independently at each occurrence a halogen atom, nitrogroup, cyano group, C₁-C₂₀ alkyl group, C₁-C₂₀ alkoxy carbonyl group,C₄-C₂₀ cycloalkyl group, or C₆-C₂₀ aryl group; and t and v areindependently integers 0-5.
 27. A method according to claim 26 whereinsaid diaryl carbonate is selected from the group consisting of diphenylcarbonate, bis(4-methylphenyl)carbonate, bis(4-chlorophenyl)carbonate,bis(4-fluorophenyl)carbonate, bis(2-chlorophenyl)carbonate,bis(2,4-difluorophenyl)carbonate, bis(4-nitrophenyl)carbonate,bis(2-nitrophenyl)carbonate, and bis(methyl salicyl)carbonate.
 28. Amethod according to claim 21 wherein said contacting at least one diarylcarbonate with bisphenol A in the presence of a transesterificationcatalyst and optionally a co-catalyst, is carried out in the presence ofone or more branching agents.
 29. A method according to claim 28 whereinsaid branching agent is 1,1,1-tris(4-hydroxyphenyl)ethane.
 30. A methodaccording to claim 21 wherein said transesterification catalyst isemployed in an amount corresponding to between 1×10⁻⁸ and 2.5×10⁻⁴ molescatalyst per mole dihydroxy aromatic compound.
 31. A method according toclaim 21 wherein said co-catalyst is selected from the group consistingof quaternary ammonium compounds, quaternary phosphonium compounds, andmixtures thereof.
 32. A method according to claim 31 wherein saidquaternary ammonium compounds are selected from the group consisting oftetramethyl ammonium hydroxide and tetrabutyl ammonium hydroxide, andsaid quaternary phosphonium compounds are selected from the groupconsisting of tetrabutyl phosphonium acetate and tetrabutylphosphoniumhydroxide.
 33. A method for the preparation of bisphenol Apolycarbonate, said method comprising contacting bisphenol A withdiphenyl carbonate at a temperature in a range between about 180° C. andabout 310° C. and a pressure in a range between about 760 torr and about1 torr in the presence of a catalyst having structure IV,

and tetrabutylphosphonium acetate, said diphenyl carbonate being presentin an amount corresponding to between about 0.9 and about 1.2 molesdiphenyl carbonate per mole of bisphenol A, said catalyst havingstructure IV being present in an amount corresponding to between about1×10⁻⁸ and about 2.5×10⁻⁴ moles catalyst IV per mole bisphenol Aemployed, said tetrabutyl phosphonium acetate being present in an amountcorresponding to between about 1×10⁻⁶ and about 1×10⁻² moles tetrabutylphosphonium acetate per mole bisphenol A employed.